1. Field of the Invention
The present invention relates to a compressed powder formulation containing a substantial amount of at least one organophilic clay. The present invention also relates to a process for making the formulation.
2. Description of the Prior Art
Known antiperspirant solid formulations basically fall into four categories, namely suspensoid sticks, wax-based sticks, gelled sticks and pressed powder sticks. However, each of these types of sticks possesses certain disadvantages. A typical suspensoid or suspension stick is described in U.S. Pat. No. 4,126,679 and consists of a powdered antiperspirant active ingredient suspended in a base consisting of a fatty alcohol and a liquid siloxane. To prepare the base, the ingredients are heated to a critical temperature range, cooled at a critical rate and poured at a temperature just above the congealing point of the mass. Once the stick is cast, it will very often have voids in the middle caused by uneven cooling rates within the stick. Further processing is needed to eliminate the voids. As should be apparent from this process description, the currently marketed suspensoid sticks are both energy and time intensive.
A further type of suspensoid stick is disclosed in U.S. Pat. No. 4,440,742. The stick consists essentially of an alkali metal bicarbonate and an optional suspending agent which is dispersed in a soap which comprises a polyhydric alcohol, alone or with a monohydric alcohol, which is gelled with an alkali metal salt of a fatty acid. The suspending agent can be colloidal or pyrogenic silica, colloidal alumina, hydrophobically treated clays or colloidal magnesium aluminum silicates.
As their name indicates, wax-based sticks contain a substantial amount of wax and therefore exhibit several inherent disadvantages. The first is the difficulty of washing the wax residue left on the clothes which can cause discoloration. The second disadvantage has to do with the naturally hydrophobic character of the waxes. That is, since the commonly used active ingredients must go into solution before they exert their effects, the wax-coating of the powered antiperspirant or deodorant ingredients inhibits the perspiration from dissolving such ingredients. This naturally decreases the efficiency of the wax-based sticks.
The gelled sticks, such as based on sodium stearate as set forth in U.S. Pat. No. 4,322,400 or based on dibenzaldehyde-monosorbitol acetal as set forth in U.S. Pat. No. 4,154,816, often suffer from a stability problem when used in combination with an antiperspirant agent. The acidity of common antiperspirant agents exemplified by aluminum chlorohydrate and aluminum zirconium compounds tend to break down the sodium stearate gel structure or the dibenzaldehyde thereby deleteriously affecting the performance of the stick. In an attempt to alleviate the problem, a complexed structure of aluminum chlorohydrate and sodium chlorhydroxy lactate has been traditionally used with a sodium stearate gel, but since the compound has been rendered basic due to the sodium lactate association, it loses a significant portion of its antiperspirant activity.
Attempts have also been made in the past to provide dry, pressed powder sticks useful in the cosmetics and toiletries market. These efforts have been focused in basically two directions, the withdrawal of the processing solvents after preparation and direct-compression. The withdrawal or evaporation of the solvents after stick formation as described in U.S. Pat. No. 4,414,200 is still energy or time consuming because a suspensoid stick must still be formed before the additional process step of evaporation.
Traditional direct-compression sticks, because of the hydrophillic character of the bases used, tend to absorb water from the air or moist environments like a bathroom or human axilla. This water both swells, the base, causing it to expand and crack, and partially solubilizes any powdered active ingredients, causing a glazing of the stick surface. This glaze reduces or eliminates the payout property of the stick, largely rendering it ineffective.